Military vehicles, such as tanks and armored personnel carriers, carry large quantities of fuel. Should the fuel tank or tanks be penetrated by an enemy projectile, such as an armor-piercing shaped charge warhead, the contained fuel is likely to be instantaneously ignited in near-explosive fashion. There are in existence fire-suppresant mechanisms for such near-explosive fires. One such mechanism includes a thick-walled bottle partially filled with a liquid fire-suppressant such as Halon 1301 (bromotrifluoromethane). The liquid is pressurized to approximately 750 p.s.i.g. by direct contact with a dry pressurized gas such as nitrogen.
Certain problems exist in connection with such pre-pressurized bottle systems, as outlined for example in U.S. Pat. No. 3,915,237 issued to E. J. Rozniecki. One problem concerns slow prolonged dissolving of nitrogen into the Halon 1301, causing loss of pressurization subsequent to the initial bottle-charging operation. Another problem concerns the requirement for very accurate measurement of the nitrogen and Halon in order to achieve a desired pressure range. On a weight basis approximately 0.04 pounds of nitrogen are required for each pound of Halon 1301 in order to achieve a pressure of 750 p.s.i.g. at 70.degree. F. If the charging operation is carried out on a weight basis a very accurate weighing scale is required. If the operation is carried out on a pressure basis then corrections must be made for temperature effects; also, during the charging operation the bottle must be continually agitated to cause nitrogen to go into solution with the Halon at a satisfactory rate. Charging the bottle in the field (at a military depot) becomes a time-consuming laboratory type operation.
The existing system suffers in an operational sense in that the bottle pressure is limited by nitrogen solubility considerations, and the detracting effect of nitrogen bubbles on the flow rate of Halon out of the bottle. Also, the fact that the bottle is at a high internal pressure aggravates leakage problems and necessitates routine periodic surveillance of the bottle; otherwise the bottle will have insufficient Halon agent and pressure when it is necessary to suppress a fire.
The present invention relates to a fire-suppressant mechanism that includes a pressure-resistant bottle filled with liquid Halon 1301 at normal vapor pressure. At one of the bottle ends there is mounted a gas-generating cartridge that may be constructed as shown and described in U.S. Pat. No. 3,877,882 to Lette et al and 3,895,098 to J. F. Pietz. The cartridge includes a confined mixture of reactant particulates that are ignitable to exothermically react together and substantaneously instantaneously produce large quantities of nitrogen gas. The generated gas is confined to the space within the bottle, thereby producing an internal step pressure increase in excess of fifty atmospheres pressure, sufficient to rapidly expel the Halon 1301 through a discharge duct onto an emergent fireball. The entire sequence of events, from initial signal to the extinguisher through liquid Halon 1301 out condition, preferably takes less than 30 milliseconds.
The mechanism of this invention is advantageous in that the bottle is at Halon 1301 vapor pressure until the instant when a fire-suppressant action is required; bottle leakage problems are thereby reduced. Also, the Halon discharge rate can be somewhat greater than with the prior art system, because the expelling pressure is not limited by nitrogen-solubility factors; since the nitrogen is generated so quickly it does not have an opportunity to dissolve in the Halon or to form flow-detracting bubbles. Use of a gas-generating cartridge, as herein proposed, is also advantageous in that laborious bottle-charging operations are largely avoided. The cartridge is easily and quickly mounted on the bottle without necessity for weighing, measuring, or determining the nitrogen contents pressure or weight. Field charging operations are greatly simplified.